Terminal bushing assemblies for transformers



Dec. 23, 1958 F. A. NEWCOMBE 2,866,173

- TERMINAL Busnmc ASSEMBLIES FOR TRANSFORMERS Filed Jan. 6, 1955 2Sheets-Sheet 1 INVENTOR FfiAA/K A. A/ WcoMM TERMINAL BUSHING ASSEMBLIESFOR TRANSFORMERS Filed Jan. 6, 1955 Dec. 23,. 1958 F. A. NEWCOMBE 2Sheets-Sheet 2 INVENTOR fQ/M/K A. NEH/(OM55 W United States PatentTERMINAL BUSHING ASSEMBLIES FOR TRANSFORMERS Frank A. Newcombe, PineBluff, Ark, assignor to Central Transformer Corporation, Pine Blulf,Ark., a con poration of Arkansas Application January 6, 1955, Serial No.480,206

12 Claims. (Cl. 339-202) This invention relates to certain new anduseful improvements in terminal bushing assemblies for transformers foruse in effecting connection between incoming cables and leads fromtransformer windings. It has heretofore been considered desirable toemploy bushings for such usage in connection with transformers and inorder to connect the incoming cable and wire it has been contemplatedthat a screw-type clamp be employed for engaging the exposed end of theincoming cable and tight ly holding same against undesired removal.

Heretofore it has been considered necessary to effect such clampingthrough direct screw pressure upon the cable end which has resulted inthe undesired crimping and deformation of such cable ends causing damagethereto and at times contributing to undesired breakage of the cableends, interrupting the connection in an unsatisfactory manner. Thisproblem is particularly accentuated by the wide-spread employment ofrelatively soft metals, such as aluminum, in such cables.

The present invention is primarily directed to a new and novel terminalbushing assembly for transformers which obviates the diflicultyheretofore encountered and essentially eliminates the use of screwclamps for effecting engagement of a cable end.

The present invention contemplates the employment of a spring-operatedclamping mechanism which is effective to maintain the necessaryconnecting clamping with a minimum of pressure being exerted upon thewire, yet adequately clamping the. wire so as to hold same tightly insecure, electrical contact.

The principal object of the present invention is to provide a terminalbushing assembly for transformers which includes spring-operated meansfor clamping incoming cables in electrical communication with a windinglead.

A further object of the invention is to provide such an assembly whichincludes screw-operated means for overcoming the spring clampingpressure to effect release of the cable clamp from engagement and tocondition the assembly for reception of a cable end.

A further object of the invention is to provide in such a device meansfor preventing the accidental removal of the screw means from thebushing; and

A further object of the invention is to generally improve the design,construction and efliciency of terminal bushing assemblies fortransformers.

The means by which the foregoing and other objects of the presentinvention are accomplished and the manner of their accomplishment willreadily be understood from the following specification upon reference tothe accompanying drawings, in which: 7

Fig. 1 is a fragmentary view partly in section and partly in elevationof a terminal bushing assembly mounted horizontally in a side wall of atransformer casing.

Fig. 2 is a sectional view taken on a vertical plane along thelongitudinal axis of the bushing assembly and illustrating an incomingcable clamped by the clamping means of the assembly.

7 2,866,173 Patented Dec. 23, 1958 Fig. 3 is a fragmentary view similarto Fig. 2', but illustrating the clamping means moved into cablereleasing position. a g I Fig. 4 is a top plan view of the bushingassembly as seen in Fig. 1 with portions broken away for purposes ofillustration.

Fig. 5 is a transverse sectional view taken as on the line V-V of Fig.2.

Fig. 6 is a view similar to Fig. 5 with the bushing assembly rotateddegrees from the position of Fig. 5.

Fig. 7 is a transverse sectional view taken as on the line VII-VII ofFig. 2; and

Fig. 8 is a transverse sectional view taken as on the line VHIVII1 ofFig. 2.

Referring now to the drawings in which the various parts are indicatedby numerals, the terminal bushing assembly 19 of the present inventionis illustrated as mounted in an opening formed in a side wall 11 of atransformer casing 13. The bushing assembly 10 includes a bushing body15, preferably of porcelain or other suitable non-conductive material.

Bushing body 15 is provided with an inner bore or chamber 17 whichextends from the inner end of the bushing body throughout a substantialportion of the length of the body. At its outer end the body 15 isprovided with an additional bore or chamber 19 which is outwardly open.The chambers 17, 19 are preferably separated by a shoulder 21, theshoulder being preferably centrally bore-d axially of the bushing bodyto provide communication between the inner and outer chambers 17, 19.Externally body 15 is provided with an annular flange 23 which isadapted to seat in adjacency to casing side wall 11, a suitable sealinggasket 25 being interposed between fiange 23 and side wall 11 to effectseal of the bushing entrance into the casing side wall.

Adjacent its inner end and beyond flange 23 body 25 is provided with aperipheral groove 26 in which is seated a retainer spring 27 engagingand retaining a ring 29 which surrounds body 15 against removal from thebody, ring 29 being preferably undercut as at 30 to closely fit spring27. Ring 29 is preferably apertured to receive a plurality of bolts 31which are provided with lock nuts 32 and lock washers 33. The bushingbody is anchored to the casing side wall 11 by bolts 31, the bolts beingextended through ring 29 into engagement with the inner face of sideWall 11 and bearing thereagainst, pulling shoulder 23 and gasket 25 intotight sealing engagement with the side wall.

Mounted in bushing body 15 is an integral connector element 35 Which isformed of suitable conductive metal, such as a suitable grade of siliconbronze or the like and which is adapted to have a transformer leadconnected to it and to engage an incoming cable to effect electricalcommunication between the cable and lead. Connector 35 includes an outerterminal portion 37 and an inner stem portion 3 which is of reduceddiameter relative to the diameter of the terminal portion. Externallyterminal portion 37 is threaded as at 41, and, internally, adjacent itsouter end, it is chambered as at 43, chamber 43 terminating at its innerend in an annular shoulder 45, Fig. 3.

Inwardly from and in communication with chamber 43, terminal 37 islongitudinally channelled to provide a guideway 47 extendingsubstantially throughout the' remainder of the length of terminal 37 andpreferably being of substantially rectangular cross section. Terminal 37is longitudinally slotted as at 49 through its material to provideaccess to guideway 47. The terminal is additionally slotted as at 50substantially perpendicularly to slot 49 for similar purpose.Additionally the terminal 37 is transversely bored along an axisperpendicular to the plane of slot 49 to provide opposite cable openings51, the cable openings communicating with slot 50 and extending throughthe material of terminal 37.

At the; junction between terminal 37 and stem 39, connector 35 includesa disc-like annular flange 53 which is annularly grooved as at 54 toreceive and retain a sealing gasket 55. Preferably connector 35 includesa pair of diametrically opposed minor length ribs 57 which lie along aminor portion of stem 39. At its distal end stem 39 is externallythreaded as at 59 and the stem includes an internally threaded socket 60in its distal end.

Threadedly engaged with the externally threaded terminal is aninternally threaded, closed-end, hollow sleeve or cap 61, to theexterior of which is preferably fixed a protective cap 63, cap 63 beingpreferably of a nonconductive material, such as one of the suitablephenolic plastics or other suitable material. Preferably the cap 63 isof a size to extend radially beyond the open outer end of chamber 19formed in bushing body 15. Sleeve 61 is internally undercut so thatoutwardly of the threaded end portion of sleeve 61 the sleeve is spacedfrom the threads of terminal 37.

Seated on inner shoulder 45 of terminal 37 is a centrally aperturedretainer ring 65 through which extends a central plunger 67, the head ofplunger 67 being seated against the inner surface of closed sleeve 61,the sleeve 61 being preferably provided With means, such as an annularboss 68, for preventing lateral movement of the plunger relative to thesleeve. Interposed between retainer ring 65 and the head of plunger 67is a compression spring 69 urging movement of the plunger toward theinner surface of closed sleeve 61.

Beyond retainer ring 65 an eyelet block 71 is connected to plunger 67,eyelet block 71 preferably being provided with a threaded socket and thedistal end of plunger 67 being externally threaded and engaged with thesocket of the eyelet block. The eyelet block is of a size and shape toclosely and slidably fit guideway 47 and the eyelet block istransversely bored as at 73 to provide an eyelet as a cable receivingopening which may be moved into register with terminal cable openings 51for the insertion of a cable end therethrough. Preferably eyelet block71 at its inner end includes integrally formed tab members 75 whichextend transversely beyond the limits of the eyelet block and whenmounted in terminal 37, extend into terminal ca ble openings 51 andprovide means for limiting the travel slotted as at 77 through thematerial of the terminal,

and in slot 77 is loosely and slidably mounted a key 79 which is adaptedfor gravity-operation. Preferably key 79 is of substantially arcuateshape and is adapted, when terminal 37 is turned to position slot 77facing downwardly, to drop through slot 77 and seat against the undercutportion of closed sleeve 61, thus extending radially beyond the threadsof terminal 37 and preventing relative movement of the cap and sleevethere-- beyond.

In the assembly of the device eyelet block 71 is introduced throughlongitudinal slot 49 into guideway 47, cross slot 50 providing for theentry of tabs 75 therewith. Plunger 67, surrounded by spring 69, isinserted through the central aperture of retainer ring 65 and engagedwith eyelet block 71, preferably in the manner described. Sleeve 61 withcap 63 may then be engaged with the exterior threads of terminal 37 andwith the terminal positioned so as to retain key 79 within slot 77, thecap and sleeve 61 may be rotated and run down beyond slot 77. Thus theconnector and the spring-operated eyelet, together with the protectivecap, are assembled together.

Connector stem 39 is then inserted through the central bore formed inshoulder 21, the bore being preferably radially undercut to accommodateterminal ribs 57, the ribs effectively keying the connector to thebushing body against relative rotation. Gasket 55 is brought intoengagement with the outer face of shoulder 21. A washer 81 is passedover the threaded end of stem 39 and a nut 83 is engaged with theexternal threads of stem 39 and is moved into tight fitting engagementwith the inner face of shoulder 21, thus fixing the connector to thebushing body against withdrawal. When so positioned it will be observedthat it is preferred that slot 77 of terminal 37 be positioneddownwardly so that key 79 drops by gravity beyond the threads ofterminal 37 as described.

The threaded end of a lead stud 85, to which is at-- tached atransformer lead 87, is then threadedly engaged with the threaded socket60 formed in the distal end of stem 39-, thus electrically connectinglead 87 to terminal 37. Bushing body 15 is preferably provided with apair of diametrically opposed cable apertures 89 which are in transversealinement with terminal cable openings 51 for selective introduction ofa cable end to the connector from the exterior. Preferably bushing body15 is additionally provided with a further aperture 91 disposedsubstantially ninety degrees from the cable apertures 89 and providingfor the reception and housing of a suitable spark rod 93, the wall ofterminal 37 being apertured substantially diametrically opposite tolongitudinal slot 49 as at 95, the aperture 95 being internally threadedand spark rod 93 being externally threaded and engaged there with.

With the terminal bushing assembly thus mounted on casing 13, anincoming cable 97 is to be introduced thereto. In so doing cap 63 isrotated, running the cap and sleeve 61 inwardly along threaded terminal37, effecting inward movement of plunger 67, and apertured eyelet block71 carried thereby, against the action of spring 69, this movement beingcontinued until the eyelet block seats against disc-like annular flange53, thus preventing further inward movement of eyelet block 71 andmoving the eyelet cable opening 73 into registry with the terminal cableopenings 51. With the openings thus in registered alinement an exposedend of incoming cable 97 may be inserted through a selected bushing bodyaperture 89 and extended through the alined eyelet and terminal cableopenings. With the cable end thus inserted in the alined cable openings,cap 63 is reversely rotated, backing the cap and sleeve 61 alongthreaded terminal 37, relaxing the force exerted on spring 69, thespring urging the plunger 67 and eyelet block 71 outwardly and effectinga tight clamping engagement of the inserted cable end, the tabs 75effecting a contact of substantial area and the cable end being movedfirmly against the outer portion of terminal cable opening 51. Reverserotation of the cap is continued until the threaded portion of sleeve 61moves into engagement with gravity-positioned key 79 by which furtherbacking off movement of the cap and sleeve is prevented.

As shown in the drawings, when the cap and sleeve have thus been backedoff along the terminal the ent1re clamping of the cable end is effectedby the action of spring 69, the sleeve 61 having been moved away fromengagement of plunger 67 and exerting no influence thereon. As isapparent in the event of wear or other change in the condition of theinserted cable end, the spring is fully effective to maintain firmclamping engagement and electrical contact with the cable end and thatthe same is accomplished Without eifecting crimplng or other deformationof the cable end, it being particularly noted that since the eyeletblock tabs 75 extend into the terminal cable openings 51, there is notendency to bend the cable end between the eyelet and the terminal.

5 It will further be observed that since the elements of connector 35,eyelet block 71, plunger 67, and closed sleeve 61 are all formed ofconductive material, a superior electrical connection is efiectedbetween incoming cable 97 and transformer lead 87. It will also beobserved that the gravity-operated key 79 is completely effective toprevent accidental removal of cap 63 and sleeve 61 from terminal 37.When, however, it becomes necessary for any reason to remove the cap andsleeve from the terminal the bushing assembly may be rotatedapproximately one hundred eighty degrees, moving slot 77 to an upperposition and causing key 79 to drop by gravity into slot 77, thusremoving from the threads of terminal 37 the previously existing limitand freeing the cap and sleeve for removal from the terminal. Iclaim:

1. In a terminal bushing assembly for transformers which includes anon-conductive bushing body adapted for mounting in a transformercasing, a conductive connector within said body extending from an outerportion of said body to an inner portion of said body and includingmeans for electrically coupling a lead, said connector in said outerportion including an externally threaded hollow terminal, internallythreaded cap means engaged with and enclosing the outer end of saidterminal, a block slidably mounted in said terminal for movementlongitudinally of said terminal, a plunger connected to said block andextending toward said cap means, spring means urging said plunger andblock outwardly toward said cap means, said terminal being transverselyapertured inwardly from said cap means to provide cable openings forreceiving endwise insertion of an incoming cable end, said block beingtransversely apertured to provide'a cable opening adapted to registerwith said terminal openings for said cable insertion, threadedadvancement of said cap means inwardly along said terminal engaging saidplunger and shifting said plunger and block against said spring meansurging inwardly toward registering alinement of said cable openings,limit means carried by said terminal blocking shift of said blockinwardly beyond cable opening registry, retraction of said cap meansoutwardly along said terminal releasing engagement of said plunger, saidspring means efiecting shift of said block away from said limit means toclampingly engage a cable end inserted into said cable openings whenregistered, said block including transversely extending tabs adjacentthe inner portion of said block cable opening, said tabs being of alength to project into said terminal cable openings to extend contactalong an inserted cable end and prevent crimping and shearing of such acable end, and means limiting cap means retracting to prevent removal ofsaid cap means from said terminal.

2. In a terminal bushing assembly for transformers which includes anon-conductive bushing body adapted for mounting in a transformercasing, a conductive connector within said body extending from an outerportion of said body to an inner portion of said body and includingmeans for electrically coupling a lead, said connector in said outerportion including an externally threaded hollow terminal, internallythreaded cap means engaged with and enclosing the outer end of saidterminal, a block slidably mounted in said terminal for movementlongitudinally of said terminal, a plunger connected to said block andextending toward said cap means, spring means merging said plunger andblock outwardly toward said cap means, said terminal being transverselyapertured inwardly from said cap means to provide cable openings forreceiving endwise insertion of an incoming cable end, said block beingtransversely apertured to provide a cable opening adapted to registerwith said terminal openings for said cable insertion, threadedadvancement of said cap means inwardly along said terminal engaging saidplunger and shifting said plunger and block against said spring meansurging inwardly toward registering alinement of said cable openings,limit means carried by said terminal blocking shift of said blockinwardly beyond cable opening registry, retraction of said cap meansoutwardly along said terminal releasing engagement of said plunger, saidspring means effecting shift of said block away from'said limit means toclampingly engage a cable end inserted into said cable openings whenregistered, said block including transversely extending tabs adjacentthe inner portion of said block cable opening, said tabs being of alength to project into said terminal cable openings to extend contactalong an inserted cable end and prevent crimping and shearing of such acable end.

3. In a terminal bushing assembly for transformers which includes anon-conductive bushing body adapted for mounting in a transformercasing, a conductive connector within said body, said connectorincluding an externally threaded hollow terminal, internally threadedcap means engaged with and enclosing the outer end of said terminal, ablock slidably mounted in said terminal for movement longitudinally ofsaid terminal, a plunger connected to said block and extending towardsaid cap means, spring means urging said plunger and block outwardlytoward said cap means, said terminal being transversely aperturedinwardly from said cap means to provide cable openings for receivingendwise insertion of an incoming cable end, said block beingtransversely apertured to provide a cable opening adapted to registerwith said terminal openings for said cable insertion, threadedadvancement of said cap means inwardly along said terminal engaging saidplunger and shifting said plunger and block against said spring meansurging inwardly toward registering alinement of said cable openings,retraction of said cap means outwardly along said terminal releasingengagement of said plunger, said spring means efiiecting shift of saidblock toward said cap means to clampingly engage a cable end insertedinto said cable openings when registered, said block includingtransversely extending tabs adjacent the inner portion of said blockcable opening, said tabs being of a length to project into said terminalcable openings to extend contact along an inserted cable end and preventcrimping and shearing of such a cable end, and means for coupling saidconnector to an electrical lead.

4. In a terminal bushing assembly for transformers which includes anon-conductive bushing body adapted for mounting in a transformercasing, a conductive connector within said body, said connectorincluding an externally threaded hollow terminal, internally threadedcap means engaged with and enclosing the outer end of said terminal, ablock slidably mounted in said terminal for movement longitudinally ofsaid terminal, a plunger connected to said block and extending towardsaid cap means, spring means urging said plunger and block outwardlytoward said cap means, said terminal being transversely aperturedinwardly from said cap means to provide cable openings for receivingendwise insertion of an incoming cable end, said block beingtransversely apertured to provide a cable opening adapted to registerwith said terminal openings for said cable insertion, threadedadvancement of said cap means inwardly along said terminal engaging saidplunger and shifting said plunger and block against said spring meansurging inwardly toward registering alinement of said cable openings,retraction of said cap means outwardly along said terminal releasingengagement of said plunger, said spring means effecting shift of saidblock toward said cap means to clampingly engage a cable end insertedinto said cable openings when registered, and means for coupling saidconnector to an electrical lead.

5. In a terminal bushing assembly, a horizontally extending, externallythreaded terminal, a screw cap mounted on and enclosing the outer end ofsaid terminal, said cap including a threaded portion adjacent its innerend threadedly engaging said terminal and outwardly therefrom beingspaced away from said terminal, said terminal adjacent its outer endbeing cut out to form a slot spaced inwardly from the outer end of saidterminal and being radially outwardly open, a curved key shiftablymounted in said slot and being gravity biased for shift relative to saidterminal, said key extending beyond the threads of said terminal intocontact with said cap when said terminal is positioned with said slotdownward and blocking disengagement of said cap from said terminal,rotation of said terminal to position said terminal with said slotupward moving said key by gravity to return within said slot and removekey blocking of cap disengagement.

6. In a terminal bushing assembly for transformers which includes anon-conductive bushing body adapted for mounting in a transformercasing, a conductive connector within said body, said connectorincluding a hollow terminal spaced at its outer end from said body, capmeans advanceably and retractably engaged with and enclosing the outerend of said terminal in the space between said terminal and said body, ablock slidably mounted in said terminal for movement longitudinally ofsaid terminal, a plunger connected to said block, spring means urgingsaid plunger outwardly toward said cap means, said terminal beingtransversely apertured inwardly from said cap means to provide cableopenings for receiving endwise insertion of an incoming cable end, saidblock being transversely apertured inwardly from said cap means toprovide a cable opening adapted to register with said terminal openingsfor said cable insertion, advancement of said cap means inwardly alongsaid terminal engaging said plunger and shifting said plunger againstsaid spring means urging inwardly toward registering alinement of saidcable openings, retractionof said cap means outwardly along saidterminal releasing engagement of said plunger, said spring meanseifecting shift of said plunger and block toward said cap means toclampingly engage a cable end inserted into said cable openings whenregistered.

7. In a terminal bushing assembly for transformers which includes anon-conductive bushing body adapted for mounting in a transformercasing, a conductive eonnector within said body, said connectorincluding a hollow terminal spaced at its outer end from said body, capmeans advanceably and retractably engaged with and enclosing the outerend of said terminal in the space between said terminal and said body, ablock slidably mounted in said terminal for movement longitudinally ofsaid terminal, a plunger connected to said block, spring means urgingsaid plunger outwardly toward said cap means, said terminal beingtransversely apertured inwardly from said cap means to provide cableopenings for receiving endwise insertion of an incoming cable end, saidblock being transversely apertured inwardly from said cap means toprovide a cable opening adapted to register with said terminal openingsfor said cable insertion, advancement of said cap means inwardly alongsaid terminal engaging said plunger and shifting said plunger againstsaid spring means urging inwardly toward registering alinement of saidcable openings, retraction of said cap means outwardly along saidterminal releasing engagement of said plunger, said spring meanseffecting shift of said plunger and block toward said cap means toclampingly engage a cable end inserted into said cable openings whenregistered, and means for coupling said connector to an electrical lead.

8. In a terminal bushing assembly, a horizontally extending terminal, acap mounted on and enclosing the outer end of said terminal, said capincluding a portion adjacent its inner end engaging said terminal andoutwardly therefrom being spaced away from said terminal, said terminalbeing cut out to form a slot spaced inwardly from the outer end of saidterminal and being radially outwardly open, a key shiftably mounted insaid slot and being gravity biased for shift relative to said terminal,said key extending beyond the periphery of said terminal into contactwith said cap when said terminal is positioned with said slot downwardand blocking disengagement of said cap from said terminal, rotation ofsaid terminal to position said terminal when said slot upward movingsaid key by gravity to return within said slot and remove key blockingof cap disengagement.

9. In a terminal bushing assembly, a substantially horizontallyextending terminal, a cap mounted on and enclosing the outer end of saidterminal, said cap including a portion adjacent its inner end engagingsaid terminal and outwardly therefrom being spaced away from saidterminal, a key shiftably mounted in the material of said terminalinwardly from the outer end of said terminal and being gravity biasedfor shift relative to said terminal, sai key extending beyond thematerial of said terminal into contact with said cap when said terminalis positioned with said key downward and blocking disengagement of saidcap fro-m said terminal, rotation of said terminal to position saidterminal with said key upward moving said key by gravity to returnwithin said terminal and remove key blocking of cap disengagement.

10. In a terminal bushing assembly, a substantially horizontallyextending, externally threaded terminal, a screw cap mounted on andenclosing the outer end of said terminal, said cap including a threadedposition adjacent its inner end threadedly engaging said terminal andoutwardly therefrom being spaced away from said terminal, said terminalbeing cut out to form a slot spaced inwardly from the outer end of saidterminal and being radially outwardly open, a key shiftably mounted insaid slot and being gravity biased for shift relative to said terminal,said key extending beyond the threads of said terminal into contact withsaid cap when said terminal is positioned with said slot downward andblocking disengagement of said cap from said terminal, rotation of saidterminal to position said terminal with said slot upward moving said keyby gravity to return within said slot and remove key blocking of capdisengagement.

11. In a terminal bushing assembly for transformers which includes anon-conductive bushing body, an elec trically conductive connectorwithin said body, said connector including a threaded hollow terminalapertured to provide openings for loosely receiving a cable end insertedtherein, plunger means slidably mounted in said terminal and aperturedadjacent its inner end to provide an opening for loosely receiving asaid cable end, said plunger means being shiftable inwardly to registerthe openings in said plunger means and said terminal, a cable endinserted through said openings, spring means within said terminalengaging said plunger means and urging said plunger outwardly, saidplunger means clampingly engaging said cable end received in saidopenings, threaded cap means threadedly engaging said threaded terminal,said cap means being threadedly advanceable inwardly along said terminalinto engagement with the outer end of said plunger means to effectinward shift of said plunger means, and said cap means being threadedlyretractable outwardly along said terminal to free said plunger means toclampingly engage said cable end, said cap means being spaced outwardlyaway from said plunger means outer end when said plunger means soengages said cable end.

12. In a terminal bushing assembly for transformers which includes anon-conductive bushing body, an electrically conductive connector withinsaid body, said connector including a threaded hollow terminal aperturedto provide openings for loosely receiving a cable end inserted therein,plunger means slidably mounted in said terminal and apertured adjacentits inner end to provide an opening for loosely receiving a said cableend, said plunger means being shiftable inwardly to register theopenings in said plunger means and said terminal, a cable end insertedthrough said openings, spring means within said terminal engaging saidplunger means and urging said plunger outwardly, said plunger meansclampingly engaging said cable end received in said openings,

9 threaded cap means threadedly engaging said threaded terminal, saidcap means being threadedly advanceable inwardly along said terminal intoengagement with the outer end of said plunger means to effect inwardshift of said plunger means, and said cap means being threadedlyretractable outwardly along said terminal to a position in which saidplunger means clampingly engages said cabie end and said cap means isspaced outwardly away from said plunger means outer end, and limit meansblocking retraction of said cap means outwardly beyond said position.

References Cited in the file of this patent UNITED STATES PATENTS

